BS 6891:2015+A1:2019

This standard BS 6891:2015+A1:2019 Specification for the installation and maintenance of low pressure gas installation pipework of up to 35 mm (R1¹₄) on premises is classified in these ICS categories:

• 91.140.40 Gas supply systems

This British Standard specifies the design, installation, commissioning and maintenance of gas installation pipework carrying 2nd and 3rd family gas of up to 35 mm (R 1¼) on premises, including residential park homes (2nd and 3rd family gas) and caravan holiday homes (2nd family gas) (see Table 1 and examples in Figure 1 to Figure 3; see also Figure 4).

NOTE 1 The principles of the standard can also be applied to the design, installation, commissioning and maintenance of gas installation pipework carrying 1st family gas.

NOTE 2 Annex A gives a method for calculating pipe sizes. Annex B discusses the sulfidation of natural gas installations, while Annex C summarizes the conclusions of a report on gas in intermediate floors. Guidance on determining whether an area can be deemed a “protected area” is given in Annex D. Requirements for LPG final stage regulator and safety devices are specified in Annex E. Annex F discusses the need for gas pipework design and installation for commercial installations to satisfy regulatory requirements regarding explosive atmospheres.

This British Standard is not applicable to:

1. service pipework and distribution systems;

2. pipework contained within an appliance;

3. bulk storage vessels;

4. LPG pipework installed in leisure accommodation vehicles and for accommodation purposes in vehicles in accordance with BS EN 1949;

5. boats, yachts and other vessels;

6. gas pipework supplying or within appliances having their own gas supply, such as mobile heaters; or

7. gas pipework supplying or within catering establishments covered by BS 6173.

Table 1 Pipework covered by BS 6891

Gas type	Pipework	Maximum nominal diameterA)	Nominal operating pressure mbarB)
2nd family (NG)	Downstream of the primary meter installation, but not downstream of the inlet of any appliance isolation valve or the inlet of the self‑sealing connector of any flexible connection	R1¼ steel, DN 35A)	21
3rd family (LPG)	Downstream of: •      the emergency control valve (ECV) located on the outside of the property where no meter is fitted; or •      the outlet of the final regulator where this is located downstream of the ECV; or •      the outlet of the final regulator where this is located downstream of any cylinders and there is no ECV; or •      the primary meter installation, but not downstream of the inlet of any appliance isolation valve or the inlet of the self‑sealing connector of any flexible connection.	R1¼ steel, DN 35A)	37 (propane) 28 (butane)

^A) Dependent upon material type.

^B) 1 bar = 105 N/m² = 100 kPa.

NOTE Unless stated otherwise:

a) the diameter for pliable corrugated (stainless-steel) tubing refers to the inside diameter; and

b) the diameter for carbon, stainless-steel tubing, copper and polyethylene (PE) refers to the outside diameter.

Figure 1 2nd family gas installation with an internal meter

Key

1	Service pipe	7	Appliance isolation valve
2	Primary meter installation	8	Appliance
3	Installation pipework	9	Part of installation within the scope of BS 6891
4	Appliance connector	R	Regulator
5	Service isolation valve (where fitted)	M	Meter
6	Emergency control valve

Figure 2 3rd family gas installation with cylinders

Key

1	Service pipework	6	Appliance isolation valve
2	Installation pipework	7	Appliance
3	Appliance connector	8	Part of installation within the scope of BS 6891
4	Cylinders	R	Regulator with over-pressure shut-off
5	Emergency control valve	ACD	Automatic changeover device

Figure 3 3rd family gas installation with bulk storage vessels

Key

1	Service pipework	6	Appliance isolation valve
2	Installation pipework	7	Appliance
3	Appliance connector	8	Part of installation within the scope of BS 6891
4	Bulk storage vessel(s)	9	Vessel isolation valve
5	Emergency control valve	R	Regulator with over-pressure shut-off

Figure 4 Selection of applicable standard(s) for gas installations

* Industrial and commercial

NOTE For commercial premises less than 35 mm, IGEM/UP/2 [12] may also be utilized.